The present invention relates, in general, to defibrillation units.
Defibrillation units have been widely used to administer one or more high-voltage, direct-current shock pulses to a patient experiencing cardiac arrest occurring because of asynchronous depolarization, i.e., fibrillation, of cardiac cells. Unconsciousness and/or death generally follow quickly after cardiac arrest. When sufficient electrical energy is delivered to the heart from a defibrillator through two or more electrodes positioned to engage the patient, fibrillation of the cardiac cells may be arrested. Thereafter, synchronous or normal depolarization of the cardiac cells will often resume.
There are two basic types of defibrillation units known in the art: external defibrillation units (which generally administer energy to a heart via electrodes placed in proximity to the surface of a patient""s body or via electrodes placed on the surface of a heart exposed during open-heart surgery) and internal defibrillation units (which generally administer energy to a heart by electrodes inserted via incisions in a patient""s body and subsequent placement of the electrodes either directly in or in extremely close proximity to the patient""s heart.)
With reference now to FIG. 1A, shown is a pictographic representation of related-art external defibrillation unit 100. Depicted are external electrodes 102, 104 which are typically positioned on a patient""s chest in the case of external defibrillation in order to deliver defibrillation energy.
External defibrillation units (e.g., external defibrillation unit 100) are often used in chaotic and stressful environments. For example, field use of defibrillators is quite common in which paramedics rush to a scene of a person who has experienced cardiac arrest. In these cases the probability for accidental misuse can be high and it is not uncommon for the external electrodes (e.g., external electrodes 102 and 104) to come in contact with each other when the defibrillation unit is on and fully charged (defibrillators often store and discharge energy via the use of storage capacitorsxe2x80x94devices which condense and store electrical energy), which effectively amounts to an electrical short circuit between the external defibrillation electrodes.
In addition, there are reports of intentional misuse by those experimenting with units who do not understand the implications of such activity and who purposely bring the electrodes in contact with each other and discharge the defibrillator.
The possibility of accidental or purposeful short circuiting of electrodes has been recognized by various regulatory agencies. As a result of such recognition, various regulatory agencies have instituted what is know as xe2x80x9cshort-circuit testing,xe2x80x9d which typically requires that an external defibrillation unit (e.g., external defibrillation unit 100) be able to withstand a certain number (e.g., ten (10)) of short-circuit discharges from a fully-charged state, where the required number of short-circuit discharges are done in rapid succession.
Referring now to FIG. 1B, shown is a pictographic representation of defibrillation unit 100 undergoing short-circuit testing in the context of two graphs 106, 108. Depicted is the little-known fact that the energy which defibrillation unit 100 is set to deliver (such setting done either internally or via controls external to defibrillation unit 100) is actually calibrated (or baselined) against an expected 50 ohm xe2x80x9cdefibrillation impedancexe2x80x9d (defibrillation impedance is a measure of how much the patient itself will impede the delivery of defibrillation energy when viewed at or near the standpoint of the source delivering the defibrillation energy.) As in the case of short-circuit testing, the amount of delivered energy to be used in dosing protocols is specified by defibrillation industry standards. For example, the American Heart Association recommends that in adults an energy level of 200 joules be set for the first defibrillation pulse, 200 or 300 joules for a second defibrillation pulse (if the first is unsuccessful), and 360 joules for a third defibrillation pulse (if the second pulse is unsuccessful)xe2x80x94all of such pulses generally baselined or calibrated for discharge through a 50-ohm defibrillation impedance.
Illustrated on graph 106 of FIG. 1B is the fact that if the energy is baselined against 50 ohms of defibrillation impedance (i.e., the unit is charged to a voltage which will deliver the specified energy into 50 ohms, e.g., graph 108), then extremely high levels of current will result within defibrillation unit 100 when defibrillation unit 100 undergoes short-circuit testing. These high levels of current are far in excess of that needed to defibrillate. The extremely high levels of current cause great strain on the electrical components of defibrillation unit 100, and can cause failure of such components. However, given the fact that approval of various regulatory agencies is extremely important in the commercial marketplace, and that such failures would be intolerable to customers, most makers of defibrillation units (e.g., defibrillation unit 100) have generated a solution to the problems associated with the extremely high current discharges and associated electrical component stresses depicted and described in relation to FIG. 1B.
With reference now to FIG. 1C, shown is a related-art solution to the problems depicted and described in relation to FIG. 1B. Insofar as the required defibrillation energy is fixed by standards, defibrillation unit makers have had little choice in adjusting the amount of energy to be delivered into a 50 ohm impedance. Accordingly, what is commonly done in the art is to create a defibrillation unit 110, which is essentially defibrillation unit 100 modified to have high-current electrical components sufficient to withstand the extremely high short-circuit testing discharges depicted and described in relation to graph 106 of FIG. 1B.
The inventors named herein (hereinafter, inventors) have recognized that the related-art solution of FIG. 1C works well, but that such solution does have some significant associated problems. One such problem is that the high-current electrical components necessary to allow defibrillation unit 110 to pass the regulatory-agency-required short-circuit testing are expensive and difficult to obtain. Another is that permitting such high currents to flow can cause failure of such electrical components. However, the inventors have also recognized that the related art solution depicted in FIG. 1C is still the most commonly used because those in the related art have not yet discerned a way to consistently meet the regulatory-agency-required short-circuit testing and simultaneously meet the various industry standards related to the required amounts of defibrillation energy.
The present invention allows defibrillation units to consistently meet regulatory-agency-required short-circuit testing while simultaneously meeting various industry-standards related to required amounts of defibrillation energy (e.g., 360 Joules) in such a way that the unnecessarily high current electrical components of the related art are no longer necessary.
In one embodiment, a method is characterized by measuring a patient parameter associated with a human body; in response to the patient parameter, retrieving a maximum expected device parameter; and setting a limit on an energy source such that during defibrillation of the patient a defibrillation parameter associated with the maximum expected device parameter is within a defined tolerance.
In another embodiment, a method is characterized by specifying at least one device parameter limit of a defibrillation unit; and in response to the at least one specified device parameter, determining a prediction confidence level at which the device parameter limit is exceeded for one or more values of a patient parameter.
In another embodiment, a method is characterized by specifying a prediction confidence level to which a defibrillation unit device parameter is correlated with one or more values of a patient parameter; and in response to the specified prediction confidence level, determining a defibrillation unit device parameter from one or more values of a patient parameter.
In other embodiments, circuitry is used to at least partially effect the foregoing-described methods; the circuitry can include and/or utilize virtually any combination of hardware, software, and/or firmware configured to effect the foregoing-described method, depending upon the design choices of the system designer. In other embodiments, signal bearing media at least partially bear the foregoing-described methods.
The foregoing is a summary and thus contains, by necessity, simplifications, generalizations and omissions of detail; consequently, those skilled in the art will appreciate that the summary is illustrative only and is not intended to be in any way limiting. Other aspects, inventive features, and advantages of this patent application will become apparent in the non-limiting detailed description set forth below.